Known conventional catalysts for the polymerization of olefins are an .alpha.-type titanium trichloride obtained by reducing titanium tetrachloride with hydrogen, violet .gamma.-type titanium trichloride obtained by reducing titanium tetrachloride with aluminum, and .delta.-type titanium trichloride obtained by pulverizing this titanium trichloride with a ball mill. Furthermore, as the means for modifying these catalysts, methods are known in which these catalysts are mixed and pulverized with various modifiers. However, where the polymerization is carried out by using these catalysts, the polymerization activity is low and the catalysts remain in large quantities in the formed polymers, and therefore, the ash-removing step must be carried out. Recently, many proposals have been made on the preparation of solid catalyst components composed mainly of magnesium, titanium, and a halogen. In most of these proposals, however, the activity, the stereoregularity of the formed polymer, or the powder characteristic are still unsatisfactory, and further improvements are desired.
The present inventors previously proposed high-activity catalysts for the polymerization of olefins, in Japanese Examined Patent Publication No. 52-15110. In this proposal, a catalyst system having a high activity comprises (A) a catalyst component obtained by reacting metallic magnesium and a hydroxyl organic compound or an oxygen-containing compound of magnesium or the like with an oxygen-containing compound of a transition metal and an aluminum halide and (B) a catalyst component composed of an organic metal compound.
Polymer particles obtained in the presence of this catalyst have a small average particle or a broad particle size distribution, the proportion of fine particles contained in the polymer particles is large, and therefore the obtained polymer still has unsatisfactory powder characteristics. Moreover, this catalyst system is disadvantageous in that, when an .alpha.-olefin having at least 3 carbon atoms is polymerized, the ratio of formation of a stereoregular polymer is low.
The inventors carried out further research, and proposed a process for the preparation of a copolymer of ethylene with an .alpha.-olefin having at least 3 carbon atoms in Japanese Unexamined Patent Publication No. 59-58005. According to this proposal, an ethylene copolymer is obtained in a high yield by using a catalyst system comprising (A) a catalyst component obtained by reacting metallic magnesium and a hydroxyl organic compound or an oxygen-containing organic compound of magnesium or halogen-containing organic magnesium compound with an oxygen-containing organic compound of titanium or vanadium, a silicon compound, an aluminum halide compound, and a titanium tetrahalide, and (B) a catalyst component composed of an organometallic compound.
However, when an .alpha.-olefin having at least 3 carbon atoms is polymerized by using this catalyst, the obtained polymer has unsatisfactory powder characteristics and stereoregularity, and the polymerization activity is too low.
Therefore, the present inventors carried out research into the development of a process capable of providing a highly stereoregular polymer having good powder characteristics at a high yield by the polymerization of an .alpha.-olefin, especially an .alpha.-olefin having at least 3 carbon atoms.